The Role of Multilevel Landau-Zener Interference in Extreme Harmonic Generation

Motivated by the observation of multiphoton electric dipole spin resonance processes in InAs nanowires, we theoretically study the transport dynamics of a periodically driven five-level system, modeling the level structure of a two-electron double quantum dot. We show that the observed multiphoton resonances, which are dominant near interdot charge transitions, are due to multilevel Landau-Zener-Stuckelberg-Majorana interference. Here a third energy level serves as a shuttle that transfers population between the two resonant spin states. By numerically integrating the master equation we replicate the main features observed in the experiments: multiphoton resonances (as large as 8 photons), a robust odd-even dependence, and oscillations in the electric dipole spin resonance signal as a function of energy level detuning

Dielectric mismatch and shallow donor impurities in GaN/HfO2 quantum wells

In this work we investigate electron-impurity binding energy in GaN/HfO$_2$ quantum wells. The calculation considers simultaneously all energy contributions caused by the dielectric mismatch: (i) image self-energy (i.e., interaction between electron and its image charge), (ii) the direct Coulomb interaction between the electron-impurity and (iii) the interactions among electron and impurity image charges. The theoretical model account for the solution of the time-dependent Schr\"odinger equation and the results shows how the magnitude of the electron-impurity binding energy depends on the position of impurity in the well-barrier system. The role of the large dielectric constant in the barrier region is exposed with the comparison of the results for GaN/HfO$_2$ with those of a more typical GaN/AlN system, for two different confinement regimes: narrow and wide quantum wells.Comment: 6 Pages, 7 figure

Perturbation theory for the one-dimensional optical polaron

The one-dimensional optical polaron is treated on the basis of the perturbation theory in the weak coupling limit. A special matrix diagrammatic technique is developed. It is shown how to evaluate all terms of the perturbation theory for the ground-state energy of a polaron to any order by means of this technique. The ground-state energy is calculated up to the eighth order of the perturbation theory. The effective mass of an electron is obtained up to the sixth order of the perturbation theory. The radius of convergence of the obtained series is estimated. The obtained results are compared with the results from the Feynman polaron theory.Comment: 9 pages, 2 figures, RevTeX, to be published in Phys. Rev. B (2001) Ap

Enhancement of ATP levels and glucose metabolism during an infection by Chlamydia: NMR studies of living cells

The Chlamydia species are obligate intracellular bacteria that proliferate only within the infected cell. Since the extracellular bacteria are metabolically inert and there are no cell-free systems for characterizingChlamydia metabolism, we studied metabolic changes related to ATP synthesis and glycolysis in HeLa cells infected withChlamydia psittaci during the course of the 2-day infection cycle using noninvasive 31P and 13C NMR methods. We find that the infection stimulates ATP synthesis in the infected cell, with a peak of ATP levels occurring midway through the infection cycle, when most of the metabolically active bacteria are proliferating. The infection also stimulates synthesis of glutamate with a similar time course as for ATP. The stimulation is apparently due to an enhancement in glucose consumption by the infected cell, which also results in an increased rate of lactate production and glutamate synthesis as well as higher glycogen accumulation during the infection. Concurrently, infection leads to an increase in the expression of the glucose transporter, GLUT-1, on HeLa cells, which may account for the enhanced glucose consumption. The chlamydiae are thus able to stimulate glucose transport in the host cell sufficiently to compensate for the extra energy load on the cell represented by the infection

Extreme Harmonic Generation in Electrically Driven Spin Resonance

We report the observation of multiple harmonic generation in electric dipole spin resonance in an InAs nanowire double quantum dot. The harmonics display a remarkable detuning dependence: near the interdot charge transition as many as eight harmonics are observed, while at large detunings we only observe the fundamental spin resonance condition. The detuning dependence indicates that the observed harmonics may be due to Landau-Zener transition dynamics at anticrossings in the energy level spectrum.Comment: Related papers at http://pettagroup.princeton.ed

Negative photoconductance in a biased multiquantum well with filter barriers

CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOIn this paper the photon-assisted electron motion in a multiquantum well (MQW) semiconductor heterostructure in the presence of an electric field is investigated. The time-dependent Schrodinger equation is solved by using the split-operator technique to determine the photocurrent generated by the electron movement through the biased MQW system. An analysis of the energy shifts in the photocurrent spectra reveals interesting features coming from the contributions of localized and extended states on the MQW system. The photocurrent signal is found to increase for certain values of electric field, leading to the analog of the negative conductance in resonant tunneling diodes. The origin of this enhancement is traced to the mixing of localized states in the QWs with those in the continuum. This mixing appears as anticrossings between the localized and extended states and the enhanced photocurrent can be related to the dynamically induced Landau-Zener-Stuckelberg-Majorana transition between two levels at the anticrossing.In this paper the photon-assisted electron motion in a multiquantum well (MQW) semiconductor heterostructure in the presence of an electric field is investigated. The time-dependent Schrodinger equation is solved by using the split-operator technique to d893CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOsem informaçãosem informaçã